The invention relates to a control system for an automatic motor vehicle transmission with a number of gear selection modules, each of which is designed for presetting a target gear for a gear change depending on a number of operating parameters. The invention also relates to a method for operating a control system of this kind.
In a motor vehicle with an automatic transmission, in particular with an automatic stepped transmission, a control system can be used in which an automatic control unit determines a gear that is suitable for each driving situation. In this case, depending on operating parameters characteristic of the driving situation, e.g. the vehicle speed, engine speed, and/or a lateral acceleration, the best gear for the driving situation determined from these parameters, is established as the target gear. The selection of the gear suitable to be the target gear can take place in particular through evaluation of characteristic curves regarding the throttle valve position and vehicle speed stored in the control system or also through determination of an optimal engine speed and subsequent discretization, i.e. association with the gear whose speed spectrum covers the optimal engine speed. If the target gear, which is determined in this manner, differs from the currently set gear, then a shift from the current gear into the target gear can be requested and a shifting command that triggers it can be given.
Alternatively or in addition to such a presetting of the target gear, there can also be a manual presetting of a target gear, which can be activated as desired by the driver. For example, the driver can input the target gear directly by means of a selector lever. A control system for the automatic motor vehicle transmission, which system is designed to take into account such a manual input, consequently includes a number of gear selection modules, each of which is designed for presetting a target gear under different boundary conditions. A first of these gear selection modules can preset the target gear after the fashion of an automatic control by evaluating measurement values, which are characteristic for the driving situation, as operating parameters. By contrast, another gear selection module can be designed to preset the target gear based on operating parameters manually input by the driver. Furthermore, additional gear selection modules can be provided, which are respectively adapted to other driving situations or operating parameters. As soon as one of these gear selection modules, which are connected in parallel in terms of logic, presets a target gear, then a gear change into this target gear can be executed.
However, despite the fact that a target gear has just been preset by one of the gear selection modules, in certain driving situations, it can be desirable not to shift into this target gear immediately. For example, when cornering at a relatively high speed, it can be desirable not to shift gears in order to prevent possible instabilities while negotiating the curve. In another case, it can be desirable to reliably prevent so-called oscillating gear changes. Oscillating gear changes can occur when one or more of the operating parameters, which determine gear selection, changes in a way that would produce a continuous series of upshifts and downshifts.
For such situation-dependent shift prevention, the control system can include a number of analysis modules, each of which, when a respectively predeterminable operating situation occurs, generates a suppression signal to prevent a gear change. Predeterminable operating situations that can be taken into account include, for example, situations that could lead to the above-mentioned oscillating gear changes, or a situation such as xe2x80x9chigh-speed corneringxe2x80x9d. The suppression signal can be consulted in the control system in such a way as to ignore the shifting command, which is generated as a result of the presetting of a target gear by one of the gear selection modules, or to prevent this shifting command from being executed.
DE 196 24 061 A1 has disclosed a method for controlling the gear changing of an automatic motor vehicle transmission, which is designed to prevent oscillating gear changes. With this method, a shifting command to change gears into a target gear is only executed when a number of predeterminable criteria are fulfilled. In order to prevent oscillating gear changes, there is the particular provision that as one criterion, a parameter-dependent minimum waiting time must pass after a gear change is executed before a new gear change can take place. However, on the one hand this method is only aimed at preventing oscillating gear changes and on the other hand, it does not directly provide an equal treatment of several gear selection modules, which are used to preset a target gear, and consequently can be used with only a limited degree of flexibility.
The object of the invention, therefore, is to disclose a control system for an automatic motor vehicle transmission of the type mentioned above, which through a suitable use of gear change prevention means, also permits a particularly simple and transparent adaptation of the vehicle behavior to different driver requests. The object is also to disclose a method particularly suited to operating the control system.
As regards the control system, this object is attained by providing a number of analysis modules, each of which, when a respectively predeterminable operating situation occurs, generates a suppression signal to prevent a gear change, where each analysis module is associated with a respective filter element, which enables the respective suppression signal to be transmitted depending on which gear selection module has preset the target gear.
The invention is based on the realization that a particularly simple adaptation of the vehicle behavior to different requests can also be achieved by suitably combining on the one hand, a number of possible sources for the respective parameter-dependent presetting of a target gear and on the other hand, a number of possible modules for assuring the prevention of gear changes in a demand-controlled fashion. In this connection, the integration of several gear selection modules, which is embodied in the form of a parallel processing of several sources and is designed to preset the target gear, permits a target gear to be correspondingly preset in each gear selection module depending on boundary conditions specifically stored there. On the other hand, the use of a number of analysis modules permits a specific suppression of undesirable gear changes to be respectively implemented in each analysis module. However, such a multi-channel system should assure that on the one hand, a positive cooperation of all of the components is maintained and that on the other hand, mutually contradictory presets and shifting commands are reliably prevented. To that end, for each analysis module, a filter module is implemented, which from this standpoint, stops or permits the transmission of the possibly generated suppression signal. In particular, there is the provision that the origin or source of the target gear preset is taken into account in the decision governing whether a target gear preset for generating a shifting command is to be transmitted or be suppressed due to specific driving considerations.
The filter elements can each be integrated directly into the corresponding analysis modules, in the form of a decentralized design. In this instance or in an alternative possible combination of filter elements to form central filter component, a central control module can suitably control the filter elements, thus assuring a systematic and consistent cooperation of the filter elements.
For a particularly high degree of flexibility of the control system, the central control module advantageously contains information, in the form of an applicable matrix for each analysis module, which indicates the target gear-presetting gear selection module for which a possibly generated suppression signal is to be transmitted. In this embodiment, the control module is embodied in the form of a criteria administrator. The form of the applicable matrix can also be used, for example, to store information indicating that a suppression signal generated by the xe2x80x9coscillating gear change preventionxe2x80x9d analysis module is to be transmitted inside the control system if the presetting of the target gear originates from an automated control block as a gear selection module, but that the suppression signal is not to be transmitted if the presetting of the target gear originates from a selector lever as the gear selection module, which is actuated directly by the driver. Consequently, a presetting can be achieved in a particularly simple manner, which on the one hand, should reliably prevent oscillating gear changes in automatic gear selection, but which on the other hand, should immediately respond to the driver commands in manual gear selection.
Storing the association, which indicates the presetting gear selection module for which a suppression signal is to be transmitted and the analysis module to which it belongs, in the form of an applicable matrix in the central control module also assures a particularly high degree of flexibility and in particular, an ability of the control system to be used, which is not limited to the concrete vehicle type. For example, there can be a different prioritization of individual gear selection modules depending on the vehicle type: in a more sport-oriented vehicle type, for example, a manual gear presetting can be given a higher priority than an automatically generated gear presetting. In this case, when a target gear is manually preset, an oscillating gear change prevention can be suppressed, whereas when a target gear is automatically preset, an oscillating gear change prevention would be permitted. By contrast, in a vehicle type oriented more toward leisurely driving, an oscillating gear change prevention would be permitted with both manual and automatic presetting of the target gear. The control system, particularly with regard to its hardware components, can be used equally for both of these types, where the individual adaptation to the respective vehicle type can be executed merely in the form of the corresponding modification of the applicable matrix stored in the control module and can consequently be executed at a comparatively low cost.
In order to directly influence the suppression signals generated by the analysis modules, the central control module is suitably connected on the output side to each filter element associated with a respective analysis module, in order to transmit an enable signal. The enable signal can thereby xe2x80x9copenxe2x80x9d the filter element and consequently permit the transmission of a possibly existing suppression signal.
The taking into consideration of the origin of the presetting of the respective target gear can be achieved in a particularly simple manner in that, in an advantageous embodiment, each gear selection module, in chronological connection with the presetting of a target gear, respectively sends a signal, which identifies the presetting gear selection module, to the filter elements or to the central control module.
As regards the method, the stated object is obtained by virtue of the fact that a suppression signal generated by an analysis module is enabled for transmission depending on which gear selection module has preset the target gear.
The advantages achieved with the invention are comprised in particular in that by taking the origin of a preset for a target gear into account in the decision as to whether a suppression of the gear change into this target gear in the form of a gear change prevention should take place, it is possible in a particularly simple manner for there to be a logically parallel processing of different gear selections and a logically parallel processing of different criteria for gear change preventions. In addition, by storing the corresponding association in the form of an applicable matrix in the central control module, the control system can be used in a particularly varied and flexible manner, in particular, an especially simple subsequent adaptation to modified presets as well as an ability to be used universally, even in different vehicle types.